1. Technical Field
The present invention relates to driver ICs which drive display panels and, more particularly, to a source driver IC chip which applies to each of source lines of a display panel a gradation voltage corresponding to a brightness level represented by an input video signal.
2. Description of the Related Art
Flat display panels, such as liquid crystal display panels and organic electroluminescent display panels, have a plurality of scanning lines and source lines. Each of the scanning lines is arranged to extend in a horizontal direction of a two-dimensional screen and each of the source lines is arranged to extend in a vertical direction of the two-dimensional screen. Such a display panel is mounted on a glass or film shaped substrate. Furthermore, in a peripheral region of such a display panel mounted on a substrate, a source driver is mounted which generates gradation voltages corresponding to brightness levels represented by an input video signal, and applies driving pulses corresponding to the gradation voltages to the respective source lines of the display panel.
As such a source driver, a source driver is known which includes a gradation voltage generating circuit which generates a plurality of gradation voltages as described above (see, for example, FIGS. 2 and 3 of Japanese Patent Application Laid-Open No. 2009-15166). This gradation voltage generating circuit is configured to generate gradation voltages (V1 to Vn) by amplifying a plurality of externally supplied reference gradation voltages (VE1 to VEm) in operational amplifiers (23k to 23m) respectively and applying the amplified voltages to respective input taps of a resistance ladder (24) respectively.
Recently, a source driver is also known which is divided into a plurality of source driver IC chips (hereinafter sometimes referred to simply as “a chip” or “chips”) disposed on a periphery of a display panel, so as to cope with increase in number of source lines associated with enhancement in image resolution of a display screen (see, e.g., FIG. 3 of Japanese Patent Application Laid-Open No. 2009-15166 or FIG. 3 of Japanese Patent Application Laid-Open No. 2001-013478).
However, when a configuration is adopted that a source driver is divided into a plurality of source driver IC chips, variation in offset voltages among respective operational amplifiers of the source driver IC chips results in variation in gradation voltages among the source driver IC chips, which causes a problem of flicker in the images displayed on the display panel.
Incorporation of the above-described gradation voltage generating circuits into the respective source driver IC chips eliminates the need of external circuits and achieves cost reduction. However, a problem is that the chip size of the source driver IC chips is increased by an amount corresponding to the gradation voltage generating circuits incorporated, and it leads to increases in power consumption and heat generation.